Concrete structural members have long been recognized as providing significant advantages over structural alternatives such as steel beams, or equivalent structures. As a consequence, such members are widely used as skeletal components for precast buildings, foundation pilings, and in numerous other applications. While well adapted for such uses, particularly due to their exceptional ability to resist compression loading without damage, concrete structural members are unfortunately unable to withstand substantial tensile stressing. To a significant degree, however, this inability can be compensated for through the use of reinforcing elements such as steel reinforcing bars and strands, positioned within the concrete members, particularly through the use of longitudinal reinforcing elements that are maintained under tension until the concrete around them has set. Concrete structural members thus formed, termed "prestressed"-concrete members, are thereafter better able to resist tensile forces to which they are exposed. Such enhanced ability is particularly desirable, for example, in connection with the erection of buildings employing concrete girders and columns, since during the course of construction, or in service, the latter can be subjected to longitudinal tensile stressing, or to lateral forces which simultaneously produce tensile forces on one side of the members, and compressive forces on the other.
Similarly, in the case of concrete piling, widely used to support heavy structures including buildings, bridges, and the like, the handling, as well as the driving of the piles unavoidably involves their exposure to tensile loadings produced by lateral and other forces acting on them which the prestressing helps to resist. To reduce this exposure during handling, the piles are frequently fabricated in relatively short lengths, a strategy which not only allows lighter loads to be transported from the casting yard to the job site, but reduces the lateral loadings resulting from the heavy weight of the piles during their handling preparatory to being driven. After their arrival at the point of use, the short piles are spliced together during the installation process to form piling of the desired length.
While such expedients have greatly helped to minimize damage to concrete structural members, they are still relatively vulnerable to tensile stressing, particularly at their points of joinder with each other, as when the members are fastened together in the case of the segmented pilings described, or in multi-storied buildings in which vertical concrete columns are placed on top of each other to form the structure, and in which horizontal girders are interconnected.
In the past, a variety of methods have been proposed to accomplish such joinder or splicing, for example, plates designed to fit over the ends of the concrete members, in combination with bolts having a hollow capped collar on the end opposite their head end which allows them to be screwed onto exposed, threaded ends of reinforcing bars whose other end is anchored in the concrete members. Adjacent bars can then be connected with a "wedge" that couples the heads of bolts on adjacent bars, fastening the piles together. However, the devices are frequently unable to maintain the spliced joint under tension, such inability resulting in "play" between the connected members which results in their misalignment. Such misalignment can lead to the development of lateral forces which produce undesirable tensioning along the members. Furthermore, while the plates of the device described include a pin means to aid in centering the members over each other, the alignment thus achieved is of a "single-point" type, and the wedges can be difficult to insert at their point of installation, due to imperfect alignment.
A somewhat similar splicing device involves the use of metal end plates fixed to the end of concrete members by anchor bars fastened on one end to the plates, the other end of the bars being buried in the ends of the concrete members. Such plates also have prestressing elements attached thereto, and keyways are provided around the periphery of each of the plates into which keys are driven after abutting plates are aligned, locking the plates together. The device described is deficient, however, in that it is unable to transfer tensile forces acting between the concrete members directly across axially aligned prestressing elements. In addition, and as in the case of the prior-described device, there is no method for maintaining constant tensioning between the plates at the interface of adjacent structural members, exposing the concrete members to the possibility of stress forces generated by the misalignment resulting from play between the plates. Furthermore, and again, the keyways in the plates can be difficult to align preparatory to inserting keys therein.
A number of splicing devices have been patented, including that shown in U.S. Pat. No. 3,104,532, which provides pile sections fitted with gripping head plates, and complementary gripping sleeve plates, the plates being interlocked by twisting them relative to each other after contact.
U.S. Pat. No. 3,356,398 teaches interlocking joint members designed for placement at the ends of pile members.
U.S. Pat. No. 3,422,360 contemplates the use of male and female metal caps that fit the ends of concrete piles to be drawn together. Connection is accomplished by the insertion of locking rods introduced through access passages located in one of the caps, into a recessed groove in the mating cap.
U.S. Pat. No. 3,545,214, for example, discloses building pile sections whose ends are furnished with plates that provide a male/female relationship relative to each other, allowing alignment of adjacent piles to be maintained.
U.S. Pat. No. 3,650,553 discloses plate-shaped members adapted for connection with the ends of the pile sections to be joined together. Locking wedges are provided for fastening the plate members to each other.
U.S. Pat. No. 4,009,550, shows shaped end plates secured to the ends of piles that can be locked together with locking pins. The plates are configured to have reinforcing bars attached thereto.
U.S. Pat. No. 4,314,777 illustrates piles whose ends are respectively fitted with male and female sleeves that are connected by means of a pin passed through the two sleeves following their mating, thus locking them together.
While all of the preceding accomplish splicing of the piles with which they are associated, they suffer from the lack of direct axial connection between prestressing members, as well as from a number of other deficiencies such as difficulties in achieving proper alignment, involved handling procedures, and various other problems.